Determining Electrophysiological Electrode Quality
Systems and methods are provided for simultaneously determining impedances of a plurality of electrophysiological electrodes. Signals are injected into a first electrophysiological electrode and a second electrophysiological electrode, the injected signals differing in at least one of magnitude and phase. A magnitude and phase of an output of a differential amplifier are evaluated, where the differential amplifier is responsive to outputs of the first electrophysiological electrode and the second electrophysiological electrode. An impedance of the first electrophysiological electrode and an impedance of the second electrophysiological electrode are determined based on the magnitude and the phase of the differential amplifier output.
This disclosure is related generally to electronics fault detection and more particularly to detection of electrophysiological electrode quality, such as an electrode utilized in a biomedical application.
BACKGROUNDElectrical conductors, such as electrical leads or electrodes, are often used in the acquisition and transmission of electrophysiological signals. Such signals are typically transmitted to a remote location, where the signals are stored and processed to produce useful output. For example, in an electrocardiogram system (an ECG or EKG system) a number of electrodes are placed at different positions on a human body to measure changes in electric potential across different parts of the body. Those changes in electric potential are caused by stimulus, such as the beating of the heart or respiration. Over time and usage, electrodes can age, dry out, or otherwise deteriorate, which can compromise their ability to acquire and transmit signals. For example, as ECG electrodes, often consisting of a conducting gel embedded in the middle of a self-adhesive pad, age and dry out, they become poor transducers for conversion of ionic body currents to electronic currents. As an electrode degrades, its impedance increases, and ECG signal distortion and noise increase, while transduction sensitivity correspondingly decreases. Such electrode deterioration can cause faults in signal acquisition, where deteriorated electrodes can result in limited signal capture or complete signal loss.
SUMMARYSystems and methods are provided for simultaneously determining impedances of a plurality of electrodes. Signals are injected into a first electrode and a second electrode, the injected signals differing in at least one of magnitude and phase. A magnitude and phase of an output of a differential amplifier are evaluated, where the differential amplifier is responsive to outputs of the first electrode and the second electrode. An impedance of the first electrode and an impedance of the second electrode are determined based on the magnitude and the phase of the differential amplifier output.
As another example, a system for simultaneously determining impedances of a plurality of electrodes includes a current source configured to inject signals into a first electrode and a second electrode, the injected signals differing in at least one of magnitude and phase. A differential amplifier is configured to receive an output of the first electrode and an output of the second electrode, the differential amplifier being further configured to output a difference signal. A data processor is configured to determine an impedance of the first electrode and an impedance of the second electrode based on a magnitude and phase of the difference signal.
As a further example, an electrocardiogram machine is configured to determine impedances of a plurality of electrodes connected to the electrocardiogram machine, signals that differ in at least one of magnitude and phase being injected into a first electrode and a second electrode. The electrocardiogram machine includes a differential amplifier configured to receive an output of the first electrode and an output of the second electrode, the differential amplifier being further configured to output a difference signal. A data processor is configured to determine an impedance of the first electrode and an impedance of the second electrode based on a magnitude and phase of the difference signal.
The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.
Based on that analysis, the data processor 112 outputs indications 114 of the quality of the first electrode 102 and the second electrode 104. Such indications 114 can take a variety of forms. In one example, the data processor 112 outputs estimated impedance values for each of the electrodes 102, 104, where impedances within different ranges indicate different electrode qualities. In another example, the data processor 112 outputs qualitative assessments of the electrodes 102, 104, such as “Good,” “Average,” and “Bad/Replace” based on the analysis of the difference signal 110. The data processor 112 can be configured to output the quality indications 114 to a variety of destinations, such as a computer-readable memory, a user interface of an ECG machine, one or more indicator lights of an ECG machine, or a graphical user interface of a computing device (e.g., a laptop, a tablet device) that is responsive to the system, such as via a wired or wireless connection.
The circuitry within box 202 further includes a differential amplifier at 214, where the differential amplifier 214 is configured to receive outputs of both the first electrode 204 and the second electrode 206 when those electrodes are excited by the current source 212. The differential amplifier 214 generates a difference signal 216 that is indicative of the difference between the outputs of the first electrode 204 and the second electrode 206. That difference signal 216 is transmitted to a digital processing and decision making system 218 that determines the quality of the first electrode 204 and the second electrode 206 and outputs an indication of such.
In one embodiment, the differential amplifier 214 utilized to generate the difference signal 216 that is used for determining qualities of the electrodes 204, 206 is also utilized in normal device operation. For example, in an ECG machine implementation, the differential amplifier 214 depicted in
As depicted in
A system may be expanded to determine qualities of a number of additional electrodes (e.g., electrodes 226, 228), as desired. In an ECG system, typically 10 electrodes are utilized, with six of those electrodes being V-lead electrodes. Two such V-lead electrodes are depicted at 226, 228. In the example of
In one embodiment, the sampling period of the measured electrode impedance can be relatively low, not needing to be updated more than about every 30 seconds. This enables use of AC current stimulus signal magnitudes that are small, below the input referred noise level in an ECG system. Measurement signals can then be recovered via averaging, easing possible burdens of post-filtering of the ECG signal to remove the AC current “carrier wave” stimulus signals.
In certain embodiments of the disclosure, characteristics of the currents injected into the electrodes, such as by current source 212, aid in the ability of the processing system 218 to determine electrode quality. In one embodiment, the system utilizes unbalanced AC current sources injected into each electrode. The unbalanced current sources can aid in measurement of electrode impedances that change in a common mode fashion by maintaining a differential output signal even when the two corresponding electrode impedances change identically or substantially identically. In certain embodiments, if common currents were injected into electrode pairs (e.g., 204, 206), the differential amplifier (e.g., 214) would reject common mode impedance changes (and therefore common mode voltages) seen at its inputs. In one embodiment, the AC current imbalance (e.g., between I1 and I2) is at a 2:1 ratio in magnitude (e.g. I1=10 nA, I2=5 nA), where the currents are offset in phase (e.g., by 180 degrees). The currents can be designed and arranged such that there is little or no net sum current flow into the body node and neutral drive electrode 234 if desired. Currents for the V-lead electrodes 226, 228 can be similarly designed, as equal in magnitude and opposite in phase, such that the net sum of the currents into the body node 234 is zero.
As described above, each electrode of a pair of electrodes connected to a differential amplifier is injected with one of a pair of unbalanced currents. The resulting difference signal produced by the differential amplifier (following filtering, such as at the AC input current frequency F0) will have a magnitude and phase, where that magnitude and phase is indicative of the quality of both of the electrodes connected to the differential amplifier.
As described with reference to
As noted above with reference to
The reference magnitudes and phases depicted in
The table of
Examples have been used herein to describe exemplary aspects of the current subject matter, but the scope of this disclosure encompasses other examples and should not be limited thereto. For example, the frequency of the currents injected into the electrodes can be varied to facilitate measurement of various aspects of electrode impedance. In the examples described above, a mid-range frequency of 300 Hz for injected currents was utilized because that frequency facilitates measurement of both the resistive and capacitive portions of an electrode's impedance. In some implementations, separate measurement of one or both of those portions is desirable.
As described above, an electrode can be modeled as a parallel R/C circuit. Such a circuit has a corner frequency equal to 1/(2*Pi*R*C). The impedance of the electrode, Zelect, is approximately constant for input currents having a frequency below this corner frequency with a value of Zelect=R. Selecting an input current frequency near the corner frequency will facilitate measurement of a combination of the resistive and capacitive components of the impedance. Above the corner frequency, the impedance of the electrode will decrease with increasing frequency, and have a value of approximately Zelect=(1/(2*Pi*f*C)), where f is the injected current frequency. Thus, input currents having frequencies below the corner frequency will measure primarily the resistive component of the electrode impedance, and input currents above the corner frequency will measure primarily the capacitive component of the electrode.
In certain embodiments, one of the resistive and capacitive portions of the electrode impedance is more important to the electrode application. For example, where electrodes are used to sample low frequency voltage changes, such as changes caused by respiration, the electrode signal capture ability is more sensitive to capacitance changes to the electrode. Where electrodes are used to sample high frequency voltage changes, such as those caused by a heartbeat, resistance changes have a more substantial effect on the quality of electrode performance. Thus, where only one of the resistive or capacitive portions of the electrode impedance is important, a corresponding input current frequency can be selected. That is, a higher precision capacitance evaluation can be performed by injecting a high frequency current (e.g., 1000 Hz) into the electrodes. Conversely, a higher precision resistance evaluation can be performed by injecting a low frequency current (e.g., 3 Hz) into the electrodes. Reference magnitude/phase pairs as described herein would be adjusted accordingly.
In a further embodiment, a system can be configured to utilize input currents that are a composite of two frequencies IHF and ILF (e.g., IHF=1000 Hz, ILF=3 Hz). The difference signal from a differential amplifier can be band pass filtered across two different branches (i.e., one branch at 1000 Hz and a second branch at 3 Hz) to extract a magnitude and phase for each component frequency. The high frequency magnitude/phase values can be used to evaluate the capacitance of the electrode, while the low frequency magnitude/phase values can be used to evaluate the resistance of the electrode, in parallel. In certain embodiments, such a composite frequency configuration can be used to simultaneously acquire higher resolution characterizations of both the capacitive and resistive components of impedances for multiple electrodes at the same time, with limited additional hardware over other embodiments described herein.
One or more aspects or features of the subject matter described herein can be realized in digital electronic circuitry, integrated circuitry, specially designed application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) computer hardware, firmware, software, and/or combinations thereof. These various aspects or features can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. The programmable system or computing system may include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.
These computer programs, which can also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor, and can be implemented in a high-level procedural language, an object-oriented programming language, a functional programming language, a logical programming language, and/or in assembly/machine language. As used herein, the term “machine-readable medium” refers to any computer program product, apparatus and/or device, such as for example magnetic discs, optical disks, memory, and Programmable Logic Devices (PLDs), used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term “machine-readable signal” refers to any signal used to provide machine instructions and/or data to a programmable processor. The machine-readable medium can store such machine instructions non-transitorily, such as for example as would a non-transient solid-state memory or a magnetic hard drive or any equivalent storage medium. The machine-readable medium can alternatively or additionally store such machine instructions in a transient manner, such as for example as would a processor cache or other random access memory associated with one or more physical processor cores.
In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible.
The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed above. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims.
Claims
1. A method of simultaneously determining impedances of a plurality of electrophysiological electrodes, comprising:
- injecting signals into a first electrophysiological electrode and a second electrophysiological electrode, the injected signals differing in at least one of magnitude and phase;
- evaluating a magnitude and phase of an output of a differential amplifier, wherein the differential amplifier is responsive to outputs of the first electrophysiological electrode and the second electrophysiological electrode;
- wherein an impedance of the first electrophysiological electrode and an impedance of the second electrophysiological electrode are determined based on the magnitude and the phase of the differential amplifier output.
2. The method of claim 1, further comprising:
- outputting an indication of whether the impedance of either or both of the first electrophysiological electrode and the second electrophysiological electrode indicate an electrode is in a low quality state.
3. The method of claim 2, wherein electrophysiological electrodes are components of an electrocardiogram (ECG) machine, and wherein the indication indicates that an electrophysiological electrode in a low quality state is to be replaced.
4. The method of claim 1, wherein the impedance of the first electrophysiological electrode and the impedance of the second electrophysiological electrode are determined by:
- determining that both the first electrophysiological electrode and the second electrophysiological electrode have impedances that indicate that those electrodes are not in a low quality state when the magnitude of the differential amplifier output and an absolute value of the phase of the differential amplifier output are below predetermined thresholds.
5. The method of claim 1, wherein the impedance of the first electrophysiological electrode and the impedance of the second electrophysiological electrode are determined by:
- determining that both the first electrophysiological electrode and the second electrophysiological electrode have impedances that indicate that those electrodes are in a low quality state when the magnitude of the differential amplifier output exceeds a magnitude threshold and an absolute value of the phase of the differential amplifier output is below a phase threshold.
6. The method of claim 1, wherein the impedance of the first electrophysiological electrode and the impedance of the second electrophysiological electrode are determined by:
- determining that exactly one of the first electrophysiological electrode and the second electrophysiological electrode has an impedance that indicates that that one of those electrodes is in a low quality state when the magnitude of the differential amplifier output exceeds a magnitude threshold and an absolute value of the phase of the differential amplifier output exceeds a phase threshold; and
- determining which of the first electrophysiological electrode and the second electrophysiological electrode has the impedance that indicates that that electrode is in a low quality state based on whether the phase of the differential amplifier output is positive or negative.
7. The method of claim 1, wherein the impedance of the first electrophysiological electrode and the impedance of the second electrophysiological electrode are determined by comparing the magnitude and phase of the output of the differential amplifier to a plurality of reference magnitude/phase pairs and selecting a closest reference magnitude/phase pair;
- wherein each reference magnitude/phase pair indicates an impedance of the first electrophysiological electrode and the second electrophysiological electrode.
8. The method of claim 1, wherein the signals injected into the first electrophysiological electrode and the second electrophysiological electrode are comprised of a plurality of frequencies.
9. The method of claim 1, wherein the signals injected into the first electrophysiological electrode and the second electrode are composite signals having a high frequency component and a low frequency component.
10. The method of claim 9, wherein resistances of the first electrophysiological electrode and the second electrophysiological electrode are determined based on the low frequency component of the injected signals; and
- wherein capacitances of the first electrophysiological electrode and the second electrophysiological electrode are determined based on the high frequency component of the injected signals.
11. The method of claim 1, wherein the signals injected into the first electrophysiological electrode and the second electrophysiological electrode are current signals generated by a current source.
12. The method of claim 1, further comprising:
- injecting a signal into a third electrophysiological electrode;
- evaluating a magnitude and phase of an output of a second differential amplifier, wherein the second differential amplifier is responsive to an output of the third electrophysiological electrode;
- wherein an impedance of the third electrophysiological electrode is determined based on the magnitude and the phase of the second differential amplifier output.
13. The method of claim 12, wherein the second differential amplifier is further responsive to the output of the second electrophysiological electrode.
14. The method of claim 12, wherein the second differential amplifier is further responsive to a reference voltage.
15. The method of claim 14, wherein the reference voltage is a Wilson reference voltage.
16. The method of claim 12, wherein impedances of the first electrophysiological electrode, the second electrophysiological electrode, and the third electrophysiological electrode are determined at substantially the same time.
17. The method of claim 1, wherein the injected signals differ in both magnitude and phase.
18. The method of claim 1, wherein the injected signals differ in magnitude but not phase.
19. The method of claim 1, wherein the injected signals differ in phase but not magnitude.
20. A system for simultaneously determining impedances of a plurality of electrophysiological electrodes, comprising:
- a current source configured to inject signals into a first electrophysiological electrode and a second electrophysiological electrode, the injected signals differing in at least one of magnitude and phase;
- a differential amplifier configured to receive an output of the first electrophysiological electrode and an output of the second electrophysiological electrode, the differential amplifier being further configured to output a difference signal;
- a data processor configured to determine an impedance of the first electrophysiological electrode and an impedance of the second electrophysiological electrode based on a magnitude and phase of the difference signal.
21. The system of claim 20, wherein the first electrophysiological electrode and the second electrophysiological electrode are electrophysiological electrodes of an electrocardiogram machine.
22. The system of claim 21, wherein the differential amplifier is further configured to be utilized in an electrocardiogram measurement operation in addition to utilization in determining impedances of the first electrophysiological electrode and the second electrophysiological electrode.
23. The system of claim 20, wherein the current source comprises:
- a voltage source;
- a first branch comprising a first capacitor having a first capacitance;
- a second branch comprising an inverter and a second capacitor having a second capacitance that differs from the first capacitance.
24. The system of claim 20, wherein the system comprises an electrocardiogram machine.
25. An electrocardiogram machine configured to determine impedances of a plurality of electrophysiological electrodes connected to the electrocardiogram machine, signals that differ in at least one of magnitude and phase being injected into a first electrophysiological electrode and a second electrophysiological electrode, the electrocardiogram machine comprising:
- a differential amplifier configured to receive an output of the first electrophysiological electrode and an output of the second electrophysiological electrode, the differential amplifier being further configured to output a difference signal;
- a data processor configured to determine an impedance of the first electrophysiological electrode and an impedance of the second electrophysiological electrode based on a magnitude and phase of the difference signal.
26. The electrocardiogram machine of claim 25, further comprising:
- a current source for generating the signals, which differ in magnitude and phase, injected into the first electrophysiological electrode and the second electrophysiological electrode.
Type: Application
Filed: Feb 3, 2016
Publication Date: Aug 3, 2017
Inventors: Pericles Nicholas Bakalos (Maynard, MA), Ronald D. Gatzke (Lexington, MA)
Application Number: 15/014,532